We found cruising to be an outstanding way to travel with our children. It was especially great in the Baltic when we wanted to tour lots of historical sights during the day but the kids got a break in the children's program at night. If you are traveling in the summer, there should be enough kids on board for a critical mass. While we've never sailed on HAL, our favorite is Celebrity, which many people consider an "adult" line.
I strongly suggest that you research some private tours in your ports. I've just logged on here for the first time so I don't know how much port information is available here. I've found a lot at cruisecritic.com. The kids will not enjoy getting on a bus with a lot of adults and being driven from place to place. If you can arrange a private guide, your visit can be customized and paced to fit the family needs.